1. Field of the Invention
The present invention generally relates to rotary vane pumping machines, and more particularly, to a variable bandwidth striated charge for use in reducing vacuum pumping losses in a rotary vane internal combustion engine.
2. Description of Related Art
In the operation of conventional internal combustion engines in many applications (e.g. automotive), less than full power is required. It is during these partial-power situations that a great deal of an engine""s fuel efficiency can be lost. A typical automotive engine may have an efficiency of 30% at full load, but in real world driving at partial load, this efficiency often decreases to 10% or lower. It is widely accepted that reducing the partial-output efficiency losses is at least as important in improving overall fuel economy in automobiles as achieving minor improvements in peak engine efficiency at full load.
Otto cycle (spark ignition or SI) and diesel (compression ignition or CI) engines have been used extensively in automotive applications. These engines are positive displacement machines. This means that they move air at different rates in roughly linear proportion to the engine speed. The amount of air available for combustion determines the maximum amount of fuel that can be effectively burned and thus the power output. Therefore, one important way of limiting power is to reduce engine speed. Another way of limiting power at a given fuel-air ratio is to restrict the mass flow of air into the engine with a vacuum throttle. Yet another way of limiting power is to reduce fuel flow at a given engine speed and mass flow of air.
Whereas power reduction can result from any of these three methods, significant load reduction can only result from either throttling or leaning of the overall fuel-air ratio for conventional engines. In automotive applications engine speed at a given road speed is typically modified by changing the gearing in discrete steps. Engine speed is rarely continuously variable, and therefore power reduction must often be produced by load reduction alone (i.e., at least one of either throttling or leaning of the overall fuel-air ratio) in many applications such as automotive. Therefore, there exists a need to significantly improve the efficiency at partial load in internal combustion engines in these applications.
The partial-load component of efficiency losses may be broken into two primary contributors, vacuum pumping losses and mechanical friction losses. Both factors contribute significantly to the partial-load component of efficiency losses in SI engines, whereas mechanical friction losses tend to dominate the partial-load component of losses in diesel engines.
FIG. 1 is a graph of efficiency versus load for a standard SI piston engine. Line A shows the engine""s efficiency based on losses caused by fuel conversion but without considering vacuum pumping or mechanical friction losses. Line B shows the engine""s efficiency based on losses caused by fuel conversion and vacuum pumping losses. Line shows the engine""s actual efficiency based on losses caused by fuel conversion, vacuum pumping losses, and frictional losses. As FIG. 1 shows, at lower load levels, the losses in engine efficiency caused by vacuum pumping and mechanical friction losses are significant.
SI engines are typically governed by a throttle, which controls air flow. A roughly stochiometric mixture is usually required to ensure ignition and flame propagation, when initiated by a spark. Diesel engines do not have this narrow mixture requirement, and can control power output by regulating fuel flow without a throttle. The temperature of the air under high compression of a CI engine allows the robust combustion of very lean mixtures.
Although FIG. 1 describes the efficiency versus load for a standard SI piston engine, curves A and C for a standard CI engine would be roughly similar in proportion. Diesel engines have long been recognized for their improved fuel efficiency. The lack of a throttle and associated vacuum pumping losses contributes significantly to the efficiency advantage in many applications such as automotive. However, while diesel engines do not suffer from the same vacuum pumping losses as SI engines, the comparatively high compression of the diesel engine coupled with the lack of throttle increases relative friction losses from many of the rotating bearings, such as the crank, rod, and wristpin bearings.
Furthermore, the friction losses necessarily represent a greater contribution for the diesel engine than for the SI engine if both engines are constrained to the same partial load percentage. This fact can be established on a mathematical basis. By eliminating the bulk of vacuum-pumping losses, the diesel engine gains in efficiencyxe2x80x94and thus also in output. Therefore additional load reduction is required to achieve the same output. At a given speed, this additional load reduction will further increase the percentage of mechanical friction losses as the operating point moves toward the origin, in a manner similar to that shown in the curves of FIG. 1.
Therefore, one can see that by substantially reducing only one of either mechanical friction losses or vacuum pumping losses, the other remaining loss will necessarily increase as a percentage loss when constrained to the same output at a given speed. A need therefore exists for a combustion engine which substantially reduces both mechanical friction and vacuum pumping losses so as to provide a substantial improvement in partial load efficiency.
Rotary vane engines can employ roller bearings as primary frictional interfaces and therefore do not suffer from the significant sliding frictional losses of piston engines. However, this dramatic reduction of friction means a larger percentage of the partial load inefficiency comes from vacuum pumping losses in a throttled engine when constrained to the same load, for the mathematical reasons described above. An engine that could simultaneously significantly reduce or substantially eliminate both mechanical friction and vacuum pumping losses at partial loads would offer significant efficiency advantages for many applications such as automotive. A need therefore exists for a low-friction rotary-vane combustion engine that employs a means to significantly eliminate vacuum pumping losses while maintaining the ability to rapidly adjust the load across a wide range of load outputs.
One variety of rotary engines that could be configured under the present invention to avoid vacuum pumping losses are rotary vane combustion engines (more particularly, rotary vane internal combustion engines). This class of rotary vane pumping machine includes designs having a rotor with slots having a radial component of alignment with respect to the rotor""s axis of rotation, vanes that reciprocate within these slots, and a chamber contour within which the vane tips trace their path as they rotate and reciprocate is within their rotor slots.
The reciprocating vanes thus extend and retract synchronously with the relative rotation of the rotor and the shape of the chamber surface in such a way as to create cascading cells of compression and/or expansion, thereby providing the essential components of a pumping machine. For ease of discussion, a rotary vane combustion engine will be discussed in detail.
FIG. 2 is a side cross sectional view of a conventional rotary-vane combustion engine. FIG. 3 is an unrolled view of the cross-sectional view of FIG. 2.
As shown in FIG. 2, the rotary engine assembly includes a rotor 10, a chamber ring assembly 20, and left and right linear translation ring assembly plates 30.
The rotor 10 includes a rotor shaft 11, and the rotor 10 rotates about the central axis of the rotor shaft 11 in a counterclockwise direction as shown by arrow xe2x80x9cRxe2x80x9d in FIG. 2. The rotor 10 has a rotational axis, at the axis of the rotor shaft 11, that is fixed relative to a stator cavity 21 contained in the chamber ring assembly 20.
The rotor 10 houses a plurality of vanes 12 in vane slots 13, and each pair of log adjacent vanes 12 defines a vane cell 14. The contoured stator 21 forms the roughly circular shape of the chamber outer surface. Pairs of opposing vanes 12 are preferably connected through the rotor 10, but may be separate.
The linear translation ring assembly plates 30 are disposed at each axial end of the chamber ring assembly 20, and at least one of the linear translation ring assembly plates includes a linear translation ring 31. The linear translation ring 31 itself spins freely around a fixed hub 32 located in the linear translation ring assembly plate 30, with the axis of the fixed hub 32 being eccentric to the axis 33 of rotor shaft 11. The linear translation ring 31 contains a plurality of linear channels or facets 34 formed on its outer surface 35. The linear channels 34 allow the vanes to move linearly as the linear translation ring 31 rotates around the fixed hub 32. The linear channels or facets 34 could be formed as a separate bearing pad or could be integral to the outer surface 35.
A hot wall combustion insert 26 may be provided along the inner surface of the a chamber ring assembly 20, preferably at or near the point of greatest compression for the vane cells 14. The hot wall combustion insert 26 is a curved surface that forms a part of the wall of the chamber ring assembly 20, along a predetermined circumference in the combustion cycle. The hot wall combustion insert 26 is preferably a ceramic insert having a near zero thermal expansion coefficient.
The hot wall combustion insert 26 is used in the combustion cycle to quickly ignite a fuel-air mixture in a combustion cycle. This hot wall combustion insert 26 maintains a temperature sufficient to combust a fuel-air mixture that is provided in a vane cell 14, and initiates combustion along the entire circumference of the hot wall combustion insert 26. Such a hot wall insert 26 allows a broad source of ignition across the entire insert permitting the robust and reliable combustion of ultra-lean fuel-air mixtures, simultaneously reducing pollution and improving efficiency.
When the present invention is used with internal combustion engines, one or more fuel or fuel-air injecting or induction devices 27 may be used and may be placed on one or both axial ends of the chamber and/or on the outer or inner circumference to the chamber. Each injector 27 may be placed at any position and angle chosen to facilitate equal distribution within the cell or vortices while preventing fuel from escaping into the exhaust stream.
Fresh air or a fuel-air charge, i.e., an intake charge, xe2x80x9cIxe2x80x9d is provided to the vane engine through an intake port formed in the chamber ring assembly 20 and/or linear translation ring assembly plates 30. Similarly, the fuel-air charge, i.e., exhaust gas, xe2x80x9cExe2x80x9d is removed from the vane engine through an exhaust port, also formed in the chamber ring assembly 20 and/or linear translation ring assembly plates 30.
A rotary scavenging disk 40 is disposed along the stator circumference, and is sized such that the rotary scavenging disk 40 extends into the vane cell 14. An outer circumferential edge of the rotary scavenging disk 40 is in sealing proximity with an outer circumferential edge of the rotor 10.
Such a rotary scavenging mechanism extends the benefits of positive-displacement scavenging and vacuum throttle capability to a two-stroke vane engine. By employing such a rotary scavenging mechanism the two-stroke vane engine reaps the efficiency and pollution benefits derived from a four-stroke design without incurring any of the associated power density and mechanical friction penalties and other tradeoffs. In addition, such a rotary scavenging mechanism provides additional or alternative benefits to certain applications, centering around the derived capability to access the vane cells at targeted positions during the pumping cycle, to purge the cell, exchange gases from/to the cell, and/or induct gases into the cell.
The illustrated rotary vane combustion engine thus employs a two-stroke cycle to maximize the power-to-weight and power-to-size ratios of the engine. The intake of the fresh air or fuel-air mixture xe2x80x9cIxe2x80x9d and the scavenging of the exhaust gas xe2x80x9cExe2x80x9d occur at the regions as shown in FIG. 2. One complete engine cycle occurs for each revolution of the rotor 10.
The vane engine shown in FIGS. 2 and 3 operates as follows.
Fresh air or a fuel-air charge is first inducted into a vane cell 14 in an intake cycle 51. Proximate to this intake cycle 51, i.e., either immediately before, during, or immediately after, fuel is combined and/or mixed with the fresh air to create a charge with a desirable fuel-to-air ratio. The mixed fuel and air charge is then compressed during a compression cycle 52, as the rotor 10 continues its motion.
As the vane chamber 14 reaches the hot wall combustion insert 26, a combustion cycle 53 is performed. During the combustion cycle 53, the air and fuel are combusted, causing a dramatic increase in heat and pressure. The initial combustion takes place as a vane cell 14 passes by the hot wall combustion insert 26 during the combustion cycle 53. This combustion involves a planar ignition that spreads radially throughout the vane chamber 14 until the air and fuel in the vane chamber 14 have been substantially combusted.
The combusted fuel and air are then expanded in an expansion cycle 54, and removed via an exhaust cycle 55. In addition, scavenging operations may be performed in the exhaust and/or intake cycles.
FIG. 3 simply shows the operation of FIG. 2 in an xe2x80x98unrolledxe2x80x99 state, in which the circular operation of the vane engine assembly is shown in a linear manner. The progression of the cycles 51, 52, 53, 54, and 55 can be seen quite effectively through FIG. 3. FIG. 3 may also be used to represent the application of the present invention in the embodiment of a vane engine in which the vanes reciprocate with an axial component of motion or in the axial direction.
Vane engines as so configured present major efficiency gains over traditional piston engines, but could benefit substantially from an improved load-adjusting device. Such vane engines derive some of their efficiency gains by using ultra-lean mixtures. As used herein, local mixture or local fuel-air ratio refers to the mixture of the primary fuel-air charge, whereas the overall mixture or ratio refers to the total proportions of air and fuel passing through the engine cells. In most conventional internal combustion engines the overall mixture and the local mixture (as previously defined) are synonymous. Typically, the load output is not primarily governed by adjusting the overall fuel-air ratio in such vane engines, because further leaning of the associated local fuel-air ratio past a point could interfere with robust combustion. Therefore, there exists a need for a low-friction rotary-vane internal combustion engine that employs a means to significantly eliminate vacuum pumping losses while maintaining the ability to rapidly adjust the load across a wide range of load outputs--and which achieves this load adjustment without requiring a throttle plate or significantly modifying the local fuel-air ratio.
Accordingly, the present invention is directed to a rotary vane combustion engine that substantially overcomes one or more of the problems due to the limitations and disadvantages of the related art.
It is a further object of the present invention to provide a rotary vane engine that can adjust the load output of the engine without a requirement to employ a vacuum throttle plate.
It is a further object of the present invention to provide a rotary vane engine that can adjust the load output of the engine without significantly altering the local fuel-air ratio of the primary fuel-air charge.
It is a further object of the present invention to provide a rotary vane engine that can adjust the load output of the engine over a wide range of loads, speeds, and operating conditions.
In the present invention, a variable bandwidth striated charge is used for inducting, compressing, combusting, expanding, and purging a fuel-air mixture within a rotary vane engine. The width of the striated fuel-air mixture in the vane rotary pump is controlled and varies depending upon the desired load output of the rotary vane engine.
To achieve these and other advantages and in accordance with the purpose of the invention, a rotary vane combustion engine is provided having a plurality of vane cells. The rotary vane combustion engine comprises a rotor having a plurality of vanes; a stator enclosing the rotor to form a plurality of vane cells between the plurality of vanes; one or more intake ports for providing an intake charge to the vane cells; one or more exhaust ports for removing exhaust gas from one of the vane cells; and a variable bandwidth fuel-air source connected to at least one of the intake ports for providing a discrete band of mixed fuel and air having a desired axial width to each of the plurality of vane cells.
The variable bandwidth fuel-air source may further comprise a variable-width intake line for providing the discrete band of mixed fuel and air with the desired axial width to each of the plurality of vane cells. Also, the one or more intake ports may further comprise one or more supplemental air lines for providing supplemental air to a portion of the plurality of vane cells not filled with the discrete band of mixed fuel and air.
The variable width intake line may itself comprise one or more first and second movable intake walls that vary the width of the discrete band of mixed fuel and air provided to each of the plurality of vane cells. The first and second movable intake walls may be attached to first and second fixed intake hinges, respectively and may each rotate or move to vary the width of the discrete band of mixed fuel and air provided to each of the plurality of vane cells. However, the first and second movable intake walls may also be moved laterally with respect to each other, such that each remains parallel to the other, to vary the width of the discrete band of mixed fuel and air provided to each of the plurality of vane cells.
The variable width intake line may also comprise one or more movable intake walls and one or more stationary intake walls. The movable intake wall may moves in relation to the stationary intake wall to vary the width of the discrete band of mixed fuel and air provided to each of the plurality of vane cells.
The variable bandwidth fuel-air source may further comprise a fuel injector attached to the variable-width intake line for receiving fuel and supplemental air and providing combined fuel and air. The variable bandwidth fuel-air source may also comprise a fixed width intake line formed between fuel injector and the variable-width intake line, and the fixed width intake line may house at least one vortex generator for mixing the combined fuel and air.
The variable bandwidth fuel-air source may further comprise a vorticity reducer downstream of the at least one vortex generator for straightening a flow of mixed fuel and air prior to induction into the vane cell. The vorticity reducer may comprise a grid of separate passages housed within the intake line through which mixed fuel and air can flow. The variable bandwidth fuel-air source may further comprise a mixing portion formed between the at least one vortex generator and the vorticity reducer to allow vortices generated by the at least one vortex generator to mix the combined fuel and air.
The one or more exhaust ports may include one or more cool air exhaust ports for removing cool supplemental air, and a combusted gas exhaust port for removing a combusted fuel-air mixture.
The combusted gas exhaust port may further comprise a variable-width exhaust line for removing the combusted fuel-air mixture from the plurality of vane cells, along an exhaust width of the vane cells. The exhaust width is preferably greater than the desired axial width of the discrete band of mixed fuel and air.
The variable width exhaust line preferably comprises one or more first and second movable walls that vary the exhaust width. The first and second movable exhaust walls may be attached to first and second fixed exhaust hinges, respectively and each may rotate to vary the exhaust width. The first and second movable exhaust walls may also be moved laterally with respect to each other, such that each remains parallel to the other, to vary the exhaust width.
The variable width exhaust line may also comprise one or more movable exhaust walls and one or more stationary exhaust walls. In this case, the movable exhaust wall moves in relation to the stationary exhaust wall to vary the exhaust width.
The rotary vane combustion engine may further comprise a catalytic converter connected to the combusted gas exhaust port. In this case, the temperature of the combusted fuel-air mixture is preferably maintained at 200xc2x0 C. or greater.
The rotary vane combustion engine may further comprise a cool air recirculation line between the one or more exhaust ports and the one or more intake ports for carrying cool air from the one or more exhaust ports to the one or more intake ports. The rotary vane combustion engine may also comprise an intercooler placed along the supplemental air recirculation line for cooling the supplemental air.